Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing

Objective. The purpose of this study was to evaluate the dynamic (storage) shear modulus and the static shear modulus of elasticity of packable and flowable composite resins and to investigate their development after initial photo-curing. Methods. Three pairs of a packable versus a flowable composite and a microfill composite resin were tested (Alert/Flow It, Filtek P60/Filtek Flow, Admira/Admira Flow, A 110). Cylindrical specimens (0.85 mm×18 mm) were made for each material. All specimens were conditioned and tested dry at 21 °C. The specimens were tested at 30 min, 24 h and 1 week after the end of photo curing. Storage shear modulus and loss tangent were determined by conducting dynamic torsional loading in the frequency range from 1 to 150 Hz. Static shear modulus measurements were made by applying a constant load (below the proportional limit of the materials) for 10 s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncanʹs Post hoc test (α=0.05). Results. Storage shear moduli (at 1 week measurement) ranged from 3.39 to 9.67 GPa, and loss tangents from 0.0735 to 0.0235; static shear moduli ranged between 2.66 and 9.80 GPa. High values of elastic moduli and low tan δ values were obtained with packable composites, while low moduli values were obtained with flowable composites. Statistically significant (α=0.05) differences were recorded between materials of the same category. Storage time, 24 h and 1 week after initial polymerization, resulted in significant increases in both moduli of elasticity. Dynamic shear storage moduli were highly correlated to the static ones (r2=0.92; P<0.05). Significance. The results of the aging studies showed that the rigidity of these materials increases significantly even 1 week after the clinician turns off the curing unit.